WEEK FIVE - Pulmonary ventilation Flashcards
Name the muscles of respiration and describe their roles in breathing
INSPIRATION = diaphragm contraction
FORCED INSPIRATION = external intercostal, pectoralis minor, sternocleidomastoid, scalenes
EXPIRATION = diaphragm relaxation
FORCED EXPIRATION = internal intercostals, rectus abdominus, internal+external oblique, transverse abdominus
Name & describe the brainstem centres that control breathing & state the inputs they receive from other levels of the NS
Breathing requires repetitive stimuli from brain for
- Skeletal muscle contraction
- Centralised control of multiple muscle
- can be VOLUNTARY OR INVOLUNTARY
[voluntary controls]
- From motor cortex –> respiratory neurons in SC
- ^ this control = overridden by alterations of O2, CO2 conc. in blood
[involuntary controls] - medulla oblongata + pons
medulla oblongata [VRG + DRG]
–VENTRAL respiratory group [VRG]
- PRIMARY generator of respiratory rhythm - innervates inspiratory+expiratory neurons
- causes contraction of diaphragm - intercostal muscles via phrenic nerve
–DORSAL respiratory group [DRG]
- INTEGRATING CENTRE for messages from pons, medulla, stretch and chemoreceptors
Influences VRG to alter respiratory rhythm
–from pons
- Pontine Respiratory Group [PRG]
= influences DRG + VRG to alter respiratory rhythm
Explain how pressure gradients account for flow in and out of the lungs, and explain how these pressure gradients are produced
Boyle’s Law : at a constant temperature, pressure in inversely proportional to volume
Charles’s Law: at a given pressure, the volume of a given quantity of gas = directly proportional to its temperature
[Air moves DOWN the gradient from high –> low pressure]
- Atmospheric pressure (PB) drives respiration
ppulm = intrapulmonary pressure
During:
[Inspiration]
VRG inspiratory neurons > contraction of diaphragm + intercostal musc. = ^ volume of thorax + ↓ ppulm to -3mm Hg > since pressure is 3mm Hg LESS than atmospheric pressure = air flows IN
[Expiration]
Diaphragm relaxes > elastic lung compression returns lung –> resting volume [EQUAL TO PB - atmospheric pressure] > ↓ in thoracic volume ^ ppulm + 3mm Hg [ 3mm Hg MORE than PB] > air flows down gradient = air from lungs –> back into environment
[forced expiration]
VRG recruits accessory respiratory muscles > contraction of abdominal muscles = ^ ppulm in thoracic cavity > ppulm can increase to +30mm Hg >
State the sources of resistance to pulmonary airflow and discuss their relevance to respiration
- PULMONARY COMPLIANCE
- how easily lungs expand
- compliance = reduced by degenerative lung disease - BRONCHIOLE DIAMETER
- PRIMARY control over resistance to airflow [bronchoconstriction/bronchodilation]
- BC = triggered by histamines, airborne irritant, parasym. stim.
- BD = triggered by symp. nerves, epinephrine - ALVEOLAR SURFACE TENSION
- thin film of water on alveolar epithelium to allow gas exchange HOWEVER it creates surface tension which acts to collapse alveoli + distal bronchioles
- offset by pulmonary surfactant - produced by type II alveolar cells
[decreases surface tension = prevents alveolar collapse]
Define anatomical dead space and relate this space to alveolar ventilation
not all inspired air reaches alveoli or undergoes gas exchange
ANATOMICAL DEAD SPACE [DSanat]
-remains in conducting zone
- usually around 150ml / ~ 2ml/kg of BW
ALVEOLAR DEAD SPACE [DSalv]
- air reaches alveoli but does NOT undergo gas exchange
PHYSIOLOGICAL DEAD SPACE
- DSanat + DSalv
ALVEOLAR VENTILATION RATE
= [tidal volume - physiological DS] x respiratory rate
Define clinical measurements of pulmonary volume and capacity
TIDAL VOLUME - VT/TV
- vol of air in one quiet breath ~ 500mL
RESIDUAL VOLUME - RV
- air remaining in lungs AFTER max expiration ~ 1300mL
- this air keeps alveoli OPEN = it cannot be breathed out
MINUTE RESPIRATORY VOLUME [MRV]
- TV x resp rate
eg 500 mL x 12 = 6L/min
- MAX voluntary ventilation = 125-170L/min
VITAL CAPACITY [VC]
- total amount of air that can be exhaled w/ effort after MAX inspiration
TOTAL LUNG CAPACITY [TLC]
- max amt of hair lungs can hold
VC = TLC - RV
TLC = VC + RV
State the diagnostic tests used for obstructive and restrictive lung disorders and state typical results found for each
Measuring ventilation can be done w/ spirometer
FVC [forced vital capacity]
Amount of air expired in a forced expiration after a maximal inspiration
FEV1 [forced expiratory volume in one second]
Amount of air expired in the first second of a forced expiration
FEV1/FVC% = SHOULD be ~80%
→ in OBSTRUCTIVE lung disease [asthma, COPD]
FEV1 = reduced but FVC can be normal
→ in RESTRICTIVE lung disease [pulmonary fibrosis]
FEV1 can be normal but FVC = reduced
Define terms for various deviations from the normal pattern of breathing
Eupnoea = Normal breathing
Dyspnea = Laboured breathing
Orthopnoea = Dyspnea in response to posture/position
Tachypnoea = Rapid + shallow breathing
Hyperpnea = Rapid + deep breathing
Kussmaul Respiration = Hyperpnea in response to acidosis
Hyperventilation = ACCELERATED breathe exceeding metabolic demand
Hypoventilation = REDUCED rate of breathing, not meeting metabolic demand
Respiratory Arrest = Permanent cessation of breathing
Define partial pressure and discuss its relationship to a gas mixture such as air (Dalton’s Law)
Pressure exerted by any one gas in mixture of gases or liquid
- one factor that determines rate of diffusion of a gas and gas exchange
DALTONS LAW
The TOTAL pressure of a gas mixture = equal to the sum of the partial pressure of its INDIVIDUAL gases
Contrast the composition of inspired and alveolar air
Differences in gas concentrations between IA and AA result from:
- Humidification of air in respiratory tract = INCREASES PH20 in AA
- Mixing of inspired and residual alveolar air = INCREASES PCO2, DECREASE PO2 in AA
- Gas exchange - INCREASE in PCO2, DECREASE in PO2 in AA
Define Henry’s Law and discuss how this law affects the gas exchange of O2 and CO2 at the lungs
HENRY’S LAW
Amount of gas that dissolves in water = determined by
its solubility in water and its partial pressure in the air
[Gases dissolve into the fluid and diffuse DOWN their concentration gradients]
- CO2 = 20x MORE soluble than O2
- O2 has ^ partial pressure gradient [greater partial pressure gradients –> ^ solubility of a gas]
- Co2 has ^ solubility
Because of this → O2 + CO2 DIFFUSE AT SAME RATE
Name and describe 5 factors that govern gas exchange between the lungs and pulmonary capillaries
- CONCETRATION GRADIENTS
- partial pressure differences at the alveoli and tissues [gas travels DOWN the gradient] - SOLUBILITY OF GAS [HENRYS LAW]
- CO2 = 20x MORE soluble than O2
- O2 has ^ partial pressure gradient [greater partial pressure gradients –> ^ solubility of a gas]
- Co2 has ^ solubility
Because of this → O2 + CO2 DIFFUSE AT SAME RATE - MEMBRANE THICKNESS
- 0.5 um thick - ^ by presence of fluid eg edema - MEMBRANE SA
- decreased SA = decreased gas exchange
- eg decreased by emphysema - VENTILATION-PERFUSION COUPLING
- BF = matched w/ airflow - MORE ventilation = vessels dilate = MORE BF
- ^ ventilation = VD
- ↓ ventilation of alveoli = VC of pulmonary ateries
State the methods in which O2 and CO2 are transported in the blood stating values for each
O2 TRANSPORT
- concentration in arterial blood - 20ml/dL
- bound to Hb as HbO2 [oxyhemoglobin] - 98.5%
- 1.5% O2 = dissolved in plasma
HbO2
- Max of 4 O2/ Hb
[when ALL 4 O2 molecules bound - HbO2 is considered 100% saturated]
- where O2 -s bound Hb becomes HbO2
CO2 TRANSPORT
- 70% = transported as HCO3 [bicarbonate ions] in plasma
- 20-25% = bound to AA group of Hb as carbaaminohemoglobin [HbCO2]
- 5-10% = dissolved in plasma as gas
Explain what the oxyhemoglobin dissociation curve shows
- Shows the relative amount of O2 saturation on Hb molecule for a given partial pressure
- The curve shows that ^ partial pressure of O2 = ^ HB saturation
- O2 UNLOADING from Hb = favoured at systemic tissues where the Po2 = LOW
- O2 LOADING –> Hb = favoured at the alveoli due to HIGH Po2
Describe how O2 and CO2 loading and unloading takes place at the tissues and the alveoli
O2 LOADING
- O2 pressure gradient = 104 mmHg [alveoli] –> 40mm Hg [blood] = pressure favours movement of of O2 from alveoli –> blood
- O2 diffuses from alveoli –> RBC –> binds w/ HHb
[O2+ HHB = HbO2 + H]
O2 UNLOADING
- O2 pressure gradient = 95 mmHg [blood] –> 40mm Hg [tissues] = pressure gradient favours movement of O2 from blood–>tissues
- H+ ions binding to HbO2 decreases O2 forming HHb
- not ALL O2 dissociates - normally one at time
- amt of O2 that remains bound to Hb = ~ 75%
CO2 LOADING
- CO2 pressure gradient 46mm Hg [tissues] –> 40mm Hg [blood] = favours movement of CO2 from tissues –> blood
- most CO2 reacts w/ water = carbonic acid > dissociates into HCO3- and H+
- HCO3- ion pumped OUT of RBC for Cl- ion IN = chloride shift
CO2 UNLOADING
- CO2 pressure gradient 46 mmHg [blood] 40mm Hg [alveoli] = CO2 from blood to alveoli
- reverse chloride shifts takes place
= HCO3- diffuses back IN –> RBC, Cl- OUT
the CO2 generated diffuses into alveolus to be exhaled
